Hydraulic fracturing is a process applied to drilled oil and gas well holes to improve the ability of fluids (such as oil and gas) to flow from the petroleum bearing formation to the drill hole. It involves injecting high pressure fracturing fluid into the rock formation with various additives, thereby causing the formation to fracture circumferentially away from the hole. During the fracturing process, the injected fracturing fluid is recovered, while the oil and gas flows from the rock formation into the drill hole and up to the well surface. The fracturing process is often necessary for economical well production.
The fractionation of water results from the fracturing process, specifically, the chemical additions that are typically used as part of the fracturing process. In the fracturing process, sand is forced under pressure into the cracks that are pressure induced into the oil or gas underground formation. The sand is carried deep into the cracks of the formation by a viscous gel. The gel is “broken” to allow the release of sand at the sand's point of furthest ingress into the formation crack. Typically, the breaking process is initiated by an enzyme breaker. Upon breaking, the fractionated water is removed from the well, and may be treated with one or more treatment methods.
Many oil and natural gas operations generate significant quantities of fractionated water, in addition to their desired hydrocarbon products. Typically, fractionated water is contaminated with significant concentrations of chemicals that require treatment before the water may be reused or discharged to the environment. Fractionated water may contain natural contaminants that are mixed with the water as a result of the fracturing process, such as hydrocarbons and inorganic salts. It may also contain synthetic contaminants, such as spent fracturing fluids including polymers and inorganic cross linking agents, polymer breaking agents, friction reduction chemicals, and lubricants. These synthetic contaminants, which are utilized in the drilling process, remain in the fractionated water upon extraction to the surface.
One method that has traditionally been used to treat fractionated water is placing it in large evaporation ponds to isolate the contaminants for later removal. However, the practice of discharging fractionated water to evaporation ponds has been recently identified as wasteful in regards to the potential benefits that might accrue from alternative uses of the water, and land.
Another disposal method that has been used for treatment of fractionated water is deep-well disposal. The advantage to deep-well disposal is that it does not waste valuable surface land area. However, deep-well disposal still results in wasting large quantities of fractionated water. Since water has become recognized as a valuable and limited resource, such wasting has become closely scrutinized. An additional disadvantage of deep-well disposal of production waters is the high cost to transport the water to the deep-well sites.
Because the limited petroleum product supply is predicted to continue, the oil and gas industry has determined that waste minimization and fractionated water treatment is the path to increased hydrocarbon production profitability and an improved social profile.
Many fractionated water treatment systems require a complete shutdown for periodic cleaning and maintenance. In addition, many fractionated water treatment systems are limited to producing a treated water stream having a certain range of total dissolved solids.
Accordingly, there remains a need for systems and methods to treat fractionated water that allow continuous production of a treated water stream with a total dissolved solids level suitable for a variety of well conditions.